Insular dwarfism

Insular dwarfism, a form of phyletic dwarfism,[1] is the process and condition of large animals evolving or having a reduced body size[a] when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf breeds, called dwarfing. This process has occurred many times throughout evolutionary history, with examples including dinosaurs, like Europasaurus, and modern animals such as elephants and their relatives. This process, and other "island genetics" artifacts, can occur not only on islands, but also in other situations where an ecosystem is isolated from external resources and breeding. This can include caves, desert oases, isolated valleys and isolated mountains ("sky islands"). Insular dwarfism is one aspect of the more general "island effect" or "Foster's rule", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies (island gigantism), and large species tend to evolve smaller bodies.

0472 - Siracusa - Museo archeologico - Elephas Falconeri Foto Giovanni Dall'Orto - 22-May-2008
Skeleton of Malta's extinct Palaeoloxodon falconeri, the smallest known species of elephant. Adult males measured about one meter in shoulder height and weighed about 305 kg. Females were considerably smaller.

Possible causes

There are several proposed explanations for the mechanism which produces such dwarfism.[3][4]

One is a selective process where only smaller animals trapped on the island survive, as food periodically declines to a borderline level. The smaller animals need fewer resources and smaller territories, and so are more likely to get past the break-point where population decline allows food sources to replenish enough for the survivors to flourish. Smaller size is also advantageous from a reproductive standpoint, as it entails shorter gestation periods and generation times.[3]

In the tropics, small size should make thermoregulation easier.[3]

Among herbivores, large size confers advantages in coping with both competitors and predators, so a reduction or absence of either would facilitate dwarfing; competition appears to be the more important factor.[4]

Among carnivores, the main factor is thought to be the size and availability of prey resources, and competition is believed to be less important.[4] In tiger snakes, insular dwarfism occurs on islands where available prey is restricted to smaller sizes than are normally taken by mainland snakes. Since prey size preference in snakes is generally proportional to body size, small snakes may be better adapted to take small prey.[5]

Dwarfism versus gigantism

The inverse process, wherein small animals breeding on isolated islands lacking the predators of large land masses may become much larger than normal, is called island gigantism. An excellent example is the dodo, the ancestors of which were normal-sized pigeons. There are also several species of giant rats, one still extant, that coexisted with both Homo floresiensis and the dwarf stegodons on Flores.

The process of insular dwarfing can occur relatively rapidly by evolutionary standards. This is in contrast to increases in maximum body size, which are much more gradual. When normalized to generation length, the maximum rate of body mass decrease during insular dwarfing was found to be over 30 times greater than the maximum rate of body mass increase for a ten-fold change in mammals.[6] The disparity is thought to reflect the fact that pedomorphism offers a relatively easy route to evolve smaller adult body size; on the other hand, the evolution of larger maximum body size is likely to be interrupted by the emergence of a series of constraints that must be overcome by evolutionary innovations before the process can continue.[6]

Factors influencing the extent of dwarfing

For both herbivores and carnivores, island size, the degree of island isolation and the size of the ancestral continental species appear not to be of major direct importance to the degree of dwarfing.[4] However, when considering only the body masses of recent top herbivores and carnivores, and including data from both continental and island land masses, the body masses of the largest species in a land mass were found to scale to the size of the land mass, with slopes of about 0.5 log(body mass/kg) per log(land area/km2).[7] There were separate regression lines for endothermic top predators, ectothermic top predators, endothermic top herbivores and (on the basis of limited data) ectothermic top herbivores, such that food intake was 7 to 24-fold higher for top herbivores than for top predators, and about the same for endotherms and ectotherms of the same trophic level (this leads to ectotherms being 5 to 16 times heavier than corresponding endotherms).[7]

Examples

Non-avian dinosaurs

Recognition that insular dwarfism could apply to dinosaurs arose through the work of Ferenc Nopcsa, a Hungarian-born aristocrat, adventurer, scholar, and paleontologist. Nopcsa studied Transylvanian dinosaurs intensively, noticing that they were smaller than their cousins elsewhere in the world. For example, he unearthed six-meter-long sauropods, a group of dinosaurs which elsewhere commonly grew to 30 meters or more. Nopcsa deduced that the area where the remains were found was an island, Hațeg Island (now the Haţeg or Hatzeg basin in Romania) during the Mesozoic era.[8][9] Nopcsa's proposal of dinosaur dwarfism on Hațeg Island is today widely accepted after further research confirmed that the remains found are not from juveniles.[10]

Sauropods

Example Species Range Timeframe Continental relatives
Ampelosaurus mount 4
Ampelosaurus
A. atacis Ibero-Armorican Island Late Cretaceous / Maastrichtian Nemegtosaurid sauropods
Europasaurus skull
Europasaurus
E. holgeri Lower Saxony Late Jurassic / Middle Kimmeridgian Brachiosaurs
Magyarosaurus- human size
Magyarosaurus
M. dacus Hateg Island Late Cretaceous / Maastrichtian Rapetosaurus
Paludititan nalatzsensis
Paludititan
P. nalatzensis Hateg Island Late Cretaceous / Maastrichtian Epachthosaurus

Other

Example Species Range Timeframe Continental relatives
Langenburg theropod size
Langenberg Quarry torvosaur
Unnamed Lower Saxony Late Jurassic / Middle Kimmeridgian Torvosaurus
Telmatosaurus sketch v2
Telmatosaurus
T. transsylvanicus Hateg Island Late Cretaceous Hadrosaurids
Tethyshadros insularis
Tethyshadros
T. insularis Trieste province Late Cretaceous Jintasaurus
Thecodontosaurus antiquus skeleton
Thecodontosaurus[9]
T. antiquus Southern England Late Triassic / Rhaetian Plateosaurus

Lufengosaurus
Zalmoxes dichotomy
Zalmoxes[9]
Z. robustus

Z. shqiperorum
Hateg Island Late Cretaceous Camptosaurus

Rhabdodon

Tenontosaurus

In addition, the genus Balaur was initially described as a Velociraptor-sized dromaeosaurid (and in consequence a dubious example of insular dwarfism), but has been since reclassified as a secondarily flightless stem bird, closer to modern birds than Jeholornis (thus actually an example of insular gigantism).

Birds

Example Binomial Name Native Range Status Continental relatives
Cozumel curassow[11] Crax rubra grisconi Cozumel Unknown Great curassow
Baudin emus
Kangaroo Island emu[12]
Dromaius novaehollandiae baudinianus Kangaroo Island, South Australia Extinct (c. AD 1827) Emu
Dromaius peroni
King Island emu[13]
Dromaius novaehollandiae minor King Island, Tasmania Extinct (AD 1822)
Cozumel thrasher[11] Toxostoma gluttatum Cozumel Critically endangered Typical thrashers

Squamates

Example Binomial Name Native Range Status Continental relatives
20150510-IMG 0786
Madagascar dwarf chameleon
Brookesia minima Nosy Be island, Madagascar Endangered Madagascar leaf chameleons
Brookesia micra on a match head
Nosy Hara chameleon[14]
Brookesia micra Nosy Hara island, Madagascar Vulnerable
Roxby Island tiger snake[5] Notechis scutatus Roxby Island, South Australia Unknown Tiger snake
Dwarf Burmese python Python bivittatus progschai Java, Bali, Sumbawa and Sulawesi, Indonesia Unknown Burmese python
Tanahjampea python[15] Python reticulatus jampeanus Tanahjampea island, between Sulawesi and Flores Unknown Reticulated python

Mammals

Pilosans

Example Binomial Name Native Range Status Continental relatives
Bradypus pygmaeus
Pygmy three-toed sloth
Bradypus pygmaeus Isla Escudo de Veraguas, Panama Critically endangered Brown-throated sloth
Habanocnus
Acratocnus
A. antillensis

A. odontrigonus

A. ye
Cuba, Hispaniola and Puerto Rico Extinct (c. 3000 BC) Megalonyx
Imagocnus I. zazae Cuba Extinct (Early Miocene)
Megalocnus
Megalocnus
M. rodens

M. zile
Cuba and Hispaniola Extinct (c. 2700 BC)
Synocnus comes
Neocnus
Neocnus spp. Cuba and Hispaniola Extinct (c. 3000 BC)

Proboscideans

Example Binomial Name Native Range Status Continental relatives
Cretanelephant-petermaas
Cretan mammoth
Mammuthus creticus Crete Extinct Mammuthus
Mammuthus exilis
Channel Islands mammoth
Mammuthus exilis Santa Rosae island Extinct (Late Pleistocene) Columbian mammoth
Sardinian mammoth Mammuthus lamarmorai Sardinia Extinct (Late Pleistocene) Steppe mammoth
Saint Paul Island woolly mammoth[16][17] Mammuthus primigenius Saint Paul Island, Alaska Extinct (c. 3750 BC) Woolly mammoth
Mammuthus falconeri (dwarf mammoth)
Siculo-Maltese elephants
Palaeoloxodon antiquus leonardi

P. mnaidriensis

P. melitensis

P. falconeri
Sicily and Malta Extinct Straight-tusked elephant
Cretan elephants Palaeoloxodon chaniensis

P. creutzburgi
Crete Extinct
Cyprus dwarf elephant Palaeoloxodon cypriotes Cyprus Extinct (c. 9000 BC)
Naxos dwarf elephant Palaeoloxodon sp. Naxos Extinct
Rhodes and Tilos dwarf elephant Palaeoloxodon tiliensis Rhodes and Tilos Extinct
Japanese stegodon[18] Stegodon aurorae Japan and Taiwan[19] Extinct (Early Pleistocene) Chinese Stegodon
Larger Flores dwarf stegodon[3] Stegodon florensis Flores Extinct (Late Pleistocene) Sundaland Stegodon
Javan dwarf stegodon[20] Stegodon hypsilophus Java Extinct
Mindanao pygmy stegodon[21] Stegodon mindanensis Mindanao and Sulawesi Extinct (Middle Pleistocene)
Sulawesi dwarf stegodon[20] Stegodon sompoensis Sulawesi Extinct
Lesser Flores dwarf stegodon[3] Stegodon sondaari Flores Extinct (Middle Pleistocene)
Sumba stegodon[22] Stegodon sumbaensis Sumba, Indonesia Extinct (Middle Pleistocene)
Timor dwarf stegodon[20] Stegodon timorensis Timor Extinct
Sambungmacan dwarf stegodon[20] Stegodon sp. Kalibeng Island (now part of Java) Extinct (Early Pleistocene)
Bumiayu tetralophodon[20] Tetralophodon bumiajuensis Bumiayu Island (now part of Java) Extinct (Early Pleistocene) Tetralophodon

Primates

Example Binomial Name Native Range Status Continental relatives
Nosy Hara dwarf lemur[23] Cheirogaleus sp. Nosy Hara island off Madagascar Unknown Dwarf lemurs
Specimen LB1
Flores Man[24]
Homo floresiensis Flores Extinct (Late Pleistocene) Homo erectus
Callao Man Homo luzonensis[25][26] Luzon, Philippines Extinct (Late Pleistocene)
Modern pygmies of Flores[27] Homo sapiens Flores Extant Humans
Early Palau modern humans (disputed)[28] Homo sapiens Palau Extinct (?)
Great Andamanese - two men - 1875
Andamanese[29][30]
Homo sapiens Andaman Islands Extant
Macaca majori
Sardinian macaque[31]
Macaca majori Sardinia Extinct (Pleistocene) Barbary macaque

Carnivorans

Example Binomial Name Native Range Status Continental relatives
Japanese Wolf
Honshū wolf
Canis lupus hodophilax Japan (excluding Hokkaido) Extinct (AD 1905) Gray wolf
Sardinian dhole Cynotherium sardous Corsica and Sardinia Extinct Xenocyon (?)
Cozumel Island coati[11] Nasua narica nelsoni Cozumel Critically endangered Yucatan white-nosed coati
Zanzibar Leopard 2
Zanzibar leopard
Panthera pardus adersi Unguja Island, Zanzibar Critically endangered or Extinct African leopard
Bali tiger zanveld
Bali tiger
Panthera tigris balica Bali Extinct (c. AD 1940) Tiger
Java Tiger
Javan tiger
Panthera tigris sondaica Java Extinct (c. AD 1975)
Cozumel Raccoon2
Cozumel raccoon
Procyon pygmaeus Cozumel Critically endangered Common raccoon
Urocyon littoralis pair
Channel Island fox
Urocyon littoralis Channel Islands of California Near Threatened Gray fox
Cozumel fox Urocyon sp. Cozumel Critically endangered or Extinct

Non-ruminant ungulates

Example Binomial Name Native Range Status Continental relatives
Malagasy Hippopotamus
Malagasy hippopotamuses
Choeropsis madagascariensis

Hippopotamus lalouema

H. lemerlei
Madagascar Extinct (c. AD 1000) Pygmy hippopotamus

Common hippopotamus
Bumiayu dwarf hippopotamus[20] Hexaprotodon simplex Bumiayu Island (now Java) Extinct (Early Pleistocene) Asian hippopotamuses
Hippopotamus cruetzburgi
Cretan dwarf hippopotamus
Hippopotamus creutzburgi Crete Extinct (Middle Pleistocene) European hippopotamus
Hippopotamus amphibius Linn at Ghar Dalam, Malta
Maltese dwarf hippopotamus
Hippopotamus melitensis Malta Extinct (Pleistocene)
Hippo-Cyprus
Cyprus dwarf hippopotamus
Hippopotamus minor Cyprus Extinct (c. 8000 BC)
Hippopotamus pentlandi 3
Sicilian hippopotamus
Hippopotamus pentlandi Sicily Extinct (Pleistocene)
Cozumel collared peccary[11] Pecari tajacu nanus Cozumel Unknown Collared peccary
Philippines rhinoceros[32] Rhinoceros philippinensis Luzon Extinct (Middle Pleistocene) Javan rhinoceros

Bovids

Example Binomial Name Native Range Status Continental relatives
Sicilian bison[18] Bison priscus siciliae Sicily Extinct (Late Pleistocene) Steppe bison
Sicilian aurochs[33] Bos primigenius siciliae[18] Sicily Extinct (Late Pleistocene) Eurasian aurochs
Cebu tamaraw Bubalus cebuensis Cebu, Philippines Extinct Wild water buffalo
Lowland anoa
Lowland anoa
Bubalus depressicornis Sulawesi and Buton, Indonesia Endangered
Bubalus mindorensis by Gregg Yan 01
Tamaraw
Bubalus mindorensis Mindoro, Philippines Critically endangered
Buablus quarlesi2
Mountain anoa
Bubalus quarlesi Sulawesi and Buton, Indonesia Endangered
Myotragus balearicus
Balearic Islands cave goat
Myotragus balearicus Majorca and Menorca Extinct (after 3000 BC) Gallogoral
Dahlak Kebir gazelle[34] Nanger soemmerringi ssp. Dahlak Kebir island, Eritrea Vulnerable Soemmerring's gazelle
Nesogoral[35] Nesogoral spp. Sardinia Extinct Gallogoral

Cervids and relatives

Example Binomial Name Native Range Status Continental relatives
Candiacervus ropalophorus
Cretan dwarf megacerine deer
Candiacervus spp. Crete Extinct (Pleistocene) Praemegaceros verticornis[9]
Ryukyu dwarf deer[36] Cervus astylodon Ryukyu Islands Extinct Sika deer (?)

Cervus praenipponicus (?)
Jersey red deer population[37] Cervus elaphus Jersey Extinct (Pleistocene) Red deer
Daino a Porto Conte archivio Marco Busdraghi AHO
Corsican red deer
Cervus elaphus corsicanus Corsica and Sardinia Near Threatened
Pleistocene Sicilian deer[18] Cervus siciliae Sicily Extinct (Late Pleistocene)
Hoplitomeryx matthei
Hoplitomeryx
Hoplitomeryx spp. Gargano Island Extinct (Early Pliocene) Pecorans
Sicilian megacerine deer[18] Megaloceros carburangelensis Sicily Extinct (Late Pleistocene) Irish elk
Key deer male
Key deer
Odocoileus virginianus clavium Florida Keys Endangered Virginia deer
Sardinian megacerine deer[9] Praemegaceros cazioti Sardinia Extinct (c. 5500 BC) Praemegaceros verticornis
Spitsbergen reindeer01
Svalbard reindeer
Rangifer tarandus platyrhynchus Svalbard Unknown Reindeer
Rusa marianna by Gregg Yan
Philippine deer
Rusa marianna Philippines Vulnerable Sambar deer

See also

Notes

  1. ^ An example of noninsular phyletic dwarfism is the evolution of the dwarfed marmosets and tamarins among New World monkeys, culminating in the appearance of the smallest example, Cebuella pygmaea.[2]

References

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  22. ^ http://ro.uow.edu.au/cgi/viewcontent.cgi?article=3055&context=smhpapers
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  24. ^ Scientist to study Hobbit morphing, abc.net.au
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  27. ^ Tucci, S.; et al. (2018-08-03). "Evolutionary history and adaptation of a human pygmy population of Flores Island, Indonesia". Science. 361 (6401): 511–516. doi:10.1126/science.aar8486. PMID 30072539.
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External links

Candiacervus

Candiacervus is an extinct genus of deer native to Pleistocene Crete. Their most notable feature, besides their peculiar, spatula-shaped antlers, was their small stature: the smallest species, C. ropalophorus, stood about 40 cm at the shoulders when fully grown, as can be inferred from a mounted skeleton. As such, the genus is considered to be a textbook example of insular dwarfism. Other features are the relatively short limbs, the massivity of the bones and the simplified antler.They were closely related to the giant Irish elk, with some experts regarding Candiacervus as a subgenus of Megaloceros.

Cyprus dwarf elephant

The Cyprus dwarf elephant (Palaeoloxodon cypriotes) is an extinct species that inhabited the island of Cyprus during the Pleistocene until around 11,000 years BC. Remains comprise 44 molars, found in the north of the island, seven molars discovered in the south-east, a single measurable femur and a single tusk among very sparse additional bone and tusk fragments. The molars support derivation from the Straight-tusked elephant (Palaeoloxodon antiquus), that inhabited Europe since 780,000 years ago, who reached the island presumably during a Pleistocene glacial maximum when low sea levels opened terrestrial corridors between Cyprus and Asia Minor. During subsequent periods of isolation the population adapted within the evolutionary mechanisms of insular dwarfism, which the available sequence of molar fossils confirms to a certain extent. The fully developed Palaeoloxodon cypriotes weighed not more than 200 kg (440 lb) and had a maximum height of 1.40 m (4.59 ft). Whether the species extinction is to be attributed to the arrival of humans on the island remains debated. The species represented a sizable food source, but was easily overcome by contemporary hunter-gatherer populations.

Cyprus dwarf hippopotamus

The Cyprus dwarf hippopotamus or Cypriot pygmy hippopotamus (Hippopotamus minor) is an extinct species of hippopotamus that inhabited the island of Cyprus until the early Holocene.

The 200-kilogram (440 lb) Cyprus dwarf hippo was roughly the same size as the extant pygmy hippopotamus. Unlike the modern pygmy hippo, the Cyprus dwarf became small through the process of insular dwarfism. This same process is believed to cause the dwarfism found in some dwarf elephants, the pygmy mammoth, and Homo floresiensis. The animal is estimated to have measured 76 cm (2.5 ft) tall and 121 cm (4.0 ft) long.H. minor is the smallest hippopotamus of all known insular hippopotamuses. The extremely small size of the hippo is in favour of a Middle Pleistocene or perhaps even Early Pleistocene colonization. At the time of its extinction between 11,000 and 9,000 years ago, the Cyprus dwarf hippo was the largest animal on the island of Cyprus. It was a herbivore and had no natural predators.Excavation sites on Cyprus, particularly Aetokremnos, provide evidence that the Cyprus dwarf hippo may have encountered and been driven to extinction by the early human residents of Cyprus.A similar species of hippo, the Cretan dwarf hippopotamus (Hippopotamus creutzburgi) existed on the island of Crete, but became extinct during the Pleistocene.

Dinosaurs of Romania

The dinosaurs of Romania are exclusively Cretaceous. Lowermost Cretaceous dinosaurs come from a bauxite mine in the Bihor County (northwest Romania) that has yielded thousands of disarticulated bones. Uppermost Cretaceous dinosaurs have been known from the Hațeg Basin (south Transylvania) since the end of the 19th century, mostly as bone concentrations (fossiliferous pockets); more recently, nests with dinosaur eggs, including hatchlings, have been found in Hațeg. Although separated by a gap of approximately 60 million years, the two dinosaur faunas from Romania share some common features: predominance of ornithopods, absence of large theropods (although the Maastrichtian Hațeg assemblage has several small theropods), and, in general, the small size of the individuals (see also insular dwarfism).

The discovery of dinosaur bones in a bauxite mine at Cornet-Brusturi, near Oradea (Bihor County) was made accidentally by two miners in 1978 during ore exploitation. Almost at the same time, research in the already known Uppermost Cretaceous dinosaur-bearing deposits from the Hațeg Basin were restarted by Dan Grigorescu, after an interruption of more than 60 years, since Franz Nopcsa’s work in the region.

The Berriasian bauxite deposits at Cornet have yielded approximately 10,000 bones and bone fragments, mainly from ornithopod dinosaurs and rarer pterosaurs. The region was located to the east of the Piemont-Liguria Ocean, and during the Early Cretaceous formed an archipelago of coral and volcanic islands, not too dissimilar to today's Indonesia or the Caribbean. As the Apulian Plate moved northwest towards the end of the Cretaceous and the beginning of the uplift of the Alpide belt, the offshore Hațeg Island was formed at the rim of the shrinking Tethys Ocean.

Among the species that lived here are: Zalmoxes, Telmatosaurus, Balaur, Rhabdodon, Magyarosaurus and Struthiosaurus. Other prehistoric creatures that lived among them, without being dinosaurs are: Allodaposuchus and Hatzegopteryx.

Dubreuillosaurus

Dubreuillosaurus is a genus of carnivorous dinosaur from the middle Jurassic Period. It is a megalosaurid theropod. Its fossils were found in France. The only named species, Dubreuillosaurus valesdunensis, was originally described as a species of Poekilopleuron, Poekilopleuron? valesdunensis, which is still formally the type species of the genus. It was later renamed Dubreuillosaurus valesdunensis when, in 2005, Allain came to the conclusion that it was not part of the genus Poekilopleuron. Its type specimen, MNHN 1998-13, is only rivalled in the number of preserved elements in this group by that of Eustreptospondylus. Dubreuillosaurus is considered to be the sister species of Magnosaurus. It did not show signs of insular dwarfism even though it was uncovered on an island.

Dwarf elephant

Dwarf elephants are prehistoric members of the order Proboscidea which, through the process of allopatric speciation on islands, evolved much smaller body sizes (around 1.5-2.3 metres) in comparison with their immediate ancestors. Dwarf elephants are an example of insular dwarfism, the phenomenon whereby large terrestrial vertebrates (usually mammals) that colonize islands evolve dwarf forms, a phenomenon attributed to adaptation to resource-poor environments and selection for early maturation and reproduction. Some modern populations of Asian elephants have also undergone size reduction on islands to a lesser degree, resulting in populations of pygmy elephants.

Fossil remains of dwarf elephants have been found on the Mediterranean islands of Cyprus, Malta (at Għar Dalam), Crete (in Chania at Vamos, Stylos and in a now underwater cave on the coast), Sicily, Sardinia, the Cyclades Islands and the Dodecanese Islands. Other islands where dwarf stegodon have been found are Sulawesi, Flores, Timor, other islands of the Lesser Sundas and Central Java, all islands are in Indonesia. The Channel Islands of California once supported a dwarf species descended from Columbian mammoths, while populations of small woolly mammoths were once found on Saint Paul Island; the mammoths on Wrangel Island are no longer considered dwarfs.

Eustreptospondylus

Eustreptospondylus ( yoo-STREPT-o-spon-DY-ləs; meaning "true Streptospondylus") is a genus of megalosaurid theropod dinosaur, from the Oxfordian stage of the Late Jurassic period (some time between 163 and 154 million years ago) in southern England, at a time when Europe was a series of scattered islands (due to tectonic movement at the time which raised the sea-bed and flooded the lowland).

Fauna of Italy

Italy has the highest level of faunal biodiversity in Europe, with over 57,000 species recorded, representing more than a third of all European fauna. This is due to various factors. The Italian peninsula is in the center of the Mediterranean Sea, forming a corridor between central Europe and North Africa, and has 8,000 km of coastline. Italy also receives species from the Balkans, Eurasia, the Middle East. Italy's varied geological structure, including the Alps and the Apennines, Central Italian woodlands, and Southern Italian Garigue and Maquis shrubland, also contribute to high climate and habitat diversity.

Foster's rule

Foster's rule, also known as the island rule or the island effect, is an ecogeographical rule in evolutionary biology stating that members of a species get smaller or bigger depending on the resources available in the environment. For example, it is known that pygmy mammoths evolved from normal mammoths on small islands. Similar evolutionary paths have been observed in elephants, hippopotamuses, boas, sloths (such as Pygmy three-toed sloth), deer (such as Key deer) and humans.The rule was first stated by J. Bristol Foster in 1964. In it, he compared 116 island species to their mainland varieties. He proposed that certain island creatures evolved into larger versions of themselves (insular gigantism) while others became smaller versions of themselves (insular dwarfism). He proposed the simple explanation that smaller creatures get larger when predation pressure is relaxed because of the absence of some of the predators of the mainland, and larger creatures become smaller when food resources are limited because of land area constraints.The idea was expanded upon in The Theory of Island Biogeography, by Robert MacArthur and Edward O. Wilson. In 1978, Ted J. Case published a longer paper on the topic in the journal Ecology.

Franz Nopcsa von Felső-Szilvás

Baron Franz Nopcsa von Felső-Szilvás (also Baron Nopcsa von Felső-Szilvás, Baron Nopcsa, Ferenc Nopcsa, báró felsőszilvási Nopcsa Ferenc, Baron Franz Nopcsa, and Franz Baron Nopcsa) (May 3, 1877 – April 25, 1933) was a Austro-Hungarian-born aristocrat, adventurer, scholar, geologist, paleontologist and albanologist. He is widely regarded as one of the founders of paleobiology, and first described the theory of insular dwarfism. He was also a specialist on Albanian studies and completed the first geological map of northern Albania.

Habayia

Habayia is an extinct genus of traversodontid cynodonts from the Late Triassic of Belgium. A single postcanine tooth was found in Habay-la-Vieille in southern Belgium. Based on the size of the tooth, Habayia was very small. Habayia lived during the Rhaetian stage of the Late Triassic at a time when western Europe was an island archipelago due to high sea levels. The small size of Habayia may be a result of insular dwarfism.

Hațeg Island

Hațeg Island was a large offshore island in the Tethys Sea which existed during the late Cretaceous period, probably from the Cenomanian to the Maastrichtian ages. It was situated in an area corresponding to the region around modern-day Hațeg, Hunedoara County, Romania. Maastrichtian fossils of small-sized dinosaurs have been found in the island's rocks.It was formed mainly by tectonic uplift during the early Alpine orogeny, caused by the collision of the African and Eurasian plates towards the end of the Cretaceous. There is no real present-day analog, but overall, the island of Hainan (off the coast of China) is perhaps closest as regards climate, geology and topography, though still not a particularly good match. The vegetation, for example, was of course entirely distinct from today, as was the fauna.

The Hungarian paleontologist Franz Nopcsa theorized that "limited resources" found on the island commonly have an effect of "reducing the size of animals" over the generations, producing a localized form of dwarfism. Nopcsa's theory of insular dwarfism—also known as the island rule—is today widely accepted.

Hon Khoai squirrel

The Hon Khoai squirrel (Callosciurus honkhoaiensis) is a species of squirrel in the family Sciuridae endemic to the small island group of Hon Khoai, which is located off the Indochinese Peninsula off the coast of south Vietnam. It can be physically differentiated from other species of Callosciurus by the hairs at the tip of the tail being white with a black base, as well as the cream-colored ventral side and feet.

This species was likely separated from the mainland by the repeated glaciations and interglaciations during the Pleistocene. Its closest relative is the gray-bellied squirrel (Callosciurus caniceps), which it diverged from as early as the Pliocene. In an example of insular dwarfism, it is much smaller than its mainland relative.

Island gigantism

Island gigantism or insular gigantism is a biological phenomenon in which the size of an animal isolated on an island increases dramatically in comparison to its mainland relatives. Island gigantism is one aspect of the more general "island effect" or "Foster's rule", which posits that when mainland animals colonize islands, small species tend to evolve larger bodies, and large species tend to evolve smaller bodies (insular dwarfism). With the arrival of humans and associated predators (dogs, cats, rats, pigs), many giant as well as other island endemics have become extinct. A similar size increase, as well as increased woodiness, has been observed in some insular plants.

Parma wallaby

The Parma wallaby (Macropus parma) was first described by British naturalist John Gould in about 1840. A shy cryptic creature of the wet sclerophyll forests of northern New South Wales (Australia), it was never commonly encountered and, even before the end of the 19th century, it was believed to be extinct.

In 1965 workers on Kawau Island (near Auckland, New Zealand) trying to control a plague of introduced tammar wallabies (a widespread and fairly common species in Australia) were astonished to discover that some of the pests were not tammar wallabies, but a miraculously surviving population of Parma wallabies—a species long thought extinct. The extermination effort was put on hold while individuals were captured and sent to institutions in Australia and around the world in the hope that they would breed in captivity and could eventually be reintroduced to their native habitat.

The renewed interest in the Parma wallaby soon led to another milestone: in 1967 it was found that they still existed in the forests near Gosford, New South Wales. Further investigation showed that the Parma wallaby was alive and well, and although not common, was to be found in forests along the Great Dividing Range from near Gosford almost as far north as the Queensland border.

The offspring of the Kawau Island population are smaller than their fully wild relatives, even when provided with ample food: it appears that competition for limited food resources on the island selected for smaller individuals, an incipient example of the phenomenon of insular dwarfism.

Phyletic dwarfism

Phyletic dwarfism is the decrease in average size of animals of a species.

There are a few circumstances that often lead to species doing this.

Lack of predators of smaller creatures can allow smaller members of a species to survive.

The lack of resources to sustain a large population of larger animals can pick off the largest specimens.

Available resources being more beneficial for smaller creatures can also do so.

These circumstances are common on islands, making insular dwarfism the most common form of phyletic dwarfism. Examples of this are the Channel Island fox, extinct dwarf elephants of Crete, and Brookesia micra, a minuscule chameleon from Madagascar. An noninsular example is the evolution of dwarfed marmosets and tamarins among New World monkeys. Phyletic dwarfism may have also helped give rise to birds from their much larger dinosaur ancestors.

Pygmy mammoth

The pygmy mammoth or Channel Islands mammoth (Mammuthus exilis) is an extinct species of dwarf elephant descended from the Columbian mammoth (M. columbi) of mainland North America. This species became extinct during the Quaternary extinction event in which many megafauna species became extinct due to changing conditions to which the species could not adapt. A case of island or insular dwarfism, from a recent analysis in 2010 it was determined that M. exilis was on average, 1.72 m (5.6 ft) tall at the shoulders and 760 kg (1,680 lb) in weight, in stark contrast to its 4.3 m (14 ft) tall, 9,070 kg (20,000 lb) ancestor. Another estimate gives a shoulder height of 2.02 m (6.6 ft) and a weight of 1,350 kg (2,980 lb).

Rampasasa

Rampasasa pygmies is a name given to a group of families described as pygmoid or Negrito, native to Waemulu village, Manggarai Regency, Flores, Indonesia, following the discovery of Homo floresiensis in the nearby Liang Bua cave in 2003.

The Rampasasa have since been reported as claiming Homo floresiensis as their ancestor and as "cashing in on hobbit craze".

A genetic study published in 2018 discounted the possibility of the Rampasasa descending from H. floresiensis, concluding that "multiple independent instances of hominin insular dwarfism occurred on Flores". However, as no genetic material from H. floresiensis was included in the analyses, any truly definitive conclusions cannot be made.

Sauropoda

Sauropoda ( or ), or the sauropods (; sauro- + -pod, "lizard-footed"), are a clade of saurischian ("lizard-hipped") dinosaurs. They had very long necks, long tails, small heads (relative to the rest of their body), and four thick, pillar-like legs. They are notable for the enormous sizes attained by some species, and the group includes the largest animals to have ever lived on land. Well-known genera include Brachiosaurus, Diplodocus, Apatosaurus, Brontosaurus, and Mamenchisaurus.Sauropods first appeared in the late Triassic Period, where they somewhat resembled the closely related (and possibly ancestral) group "Prosauropoda". By the Late Jurassic (150 million years ago), sauropods had become widespread (especially the diplodocids and brachiosaurids). By the Late Cretaceous, those groups had mainly been replaced by the titanosaurs, which had a near-global distribution. However, as with all other non-avian dinosaurs alive at the time, the titanosaurs died out in the Cretaceous–Paleogene extinction event. Fossilised remains of sauropods have been found on every continent, including Antarctica.The name Sauropoda was coined by O.C. Marsh in 1878, and is derived from Greek, meaning "lizard foot". Sauropods are one of the most recognizable groups of dinosaurs, and have become a fixture in popular culture due to their impressive size.

Complete sauropod fossil finds are rare. Many species, especially the largest, are known only from isolated and disarticulated bones. Many near-complete specimens lack heads, tail tips and limbs.

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